A conventional air conditioner is described below while referring to FIG. 24 and FIG. 25.
As shown in the drawings, a refrigeration cycle is a closed circuit comprising a compressor 101, a refrigerant discharge piping 112, a four-way valve 102, an outdoor heat exchanger 103, pressure reducing means 104a, 104b (expansion valve or capillary tube), and indoor heat exchangers 105a, 105b, all being coupled together by means of a piping 106. A refrigerant flows through the circuit. By changing over the four-way valve 102, the flow direction of the refrigerant is changed, and a cooling operation or a heating operation can be performed. In such an apparatus, recently, it has been desired to reduce the noise caused by the sound of the refrigerant due to state changes of the refrigerant flowing in the refrigeration cycle. In particular, it has been desired to reduce the noise from the pressure reducing means 104a, 104b, in which pressure changes are significant and the refrigerant is present in a gas-liquid two-phase flow, to reduce the noise from a discharge piping 112 of the compressor 101 in which pressure pulsations are large, to reduce the noise from a distributor 107 for distributing the refrigerant to the outdoor heat exchanger 103 and the indoor heat exchangers 105a, 105b uniformly, and to reduce the noise from the parts of the outdoor heat exchanger 103 and indoor heat exchangers 105a, 105b in which the piping 106 is crowded. Against these noise sources, hitherto, various noise reducing measures have been attempted.
For example, as a noise reducing measure for noise generated from the expansion valve 104a, which is one of the pressure reducing means, in Japanese Laid-open Patent No. 5-113272, a silencer combining an expansion type muffler and a porous plate is disposed in the low pressure side piping 106 of the expansion valve 104a. The expansion muffler is divided into two compartments by the porous plate, and it is designed to suppress the flowing noise of the refrigerant by adjusting the pore diameter or number of pores of the porous plate.
In Japanese Laid-open Patent No. 6-26738, a taper expanded portion is provided in the high pressure side piping 106 of the expansion valve 104a, and a porous plate is disposed in the expanded portion. In the expanded portion, bubbles of the gas refrigerant contained in the liquid refrigerant are preliminarily transformed into smaller bubbles to attenuate the energy thereof, and noise due to collision of the gas refrigerator against the expansion valve 104a is prevented.
According to Japanese Laid-open Patent No. 8-313113, a distributor 107 for diverging the refrigerant into two flows and converging them later is provided in the high pressure side piping 106 of the expansion valve 104a. By dividing and mixing the gas-liquid two-phase flow refrigerant, the liquid refrigerant and gas refrigerant are mixed uniformly, so that generation of flowing noise of the refrigerant is reduced or prevented.
In Japanese Laid-open Patent No. 9-133434, in the piping 106 before and after the expansion valve 104a, the piping diameter ratio is changed, and an expansion muffler is provided therein, or a rubber vibration absorber is wound around the piping. Sudden pressure changes are lessened by reducing the diameter of the piping 106, and the flowing noise of the refrigerant and the piping vibration noise are attenuated.
As a pulsation reducing measure of gas refrigerant coming out from the compressor 101, in Japanese Laid-open Utility Model No. 6-14685, an expansion muffler having noise absorbing bristles formed in the inner wall thereof is disposed in the discharge piping 112 of the compressor 101, wherein the motion energy of the gas refrigerant is absorbed, and resonance is prevented, so that the pulsation is decreased.
According to Japanese Laid-open Patent No. 9-250844 and Japanese Laid-open Patent No. 9-250845, an expansion muffler is provided in the discharge piping 112 of the compressor 101, and a partition board is provided in the expansion muffler. Pores are pierced in the partition board. Alternatively, plural overlapping partition boards are provided in the expansion muffler. Or, the expansion muffler is formed as a double structure. With these constructions, pulse waves of the gas refrigerant discharged from the compressor 101 are absorbed to suppress the noise.
Moreover, as a reducing measure of the noise generated from the distributor 107 for dividing the refrigerant flow, in Japanese Laid-open Patent No. 5-322379, a strainer 119 and a porous plate are disposed in the distributor 107, and the flowing noise of the refrigerant in the distributor 107 is suppressed by adjusting the pore diameter and number of pores of the porous plate.
In Japanese Laid-open Patent No. 5-118709, moreover, a silencer of a variable capacity type is disposed between a capillary tube and an indoor heat exchanger 105a. The noise frequency is detected by a microphone and a frequency analyzer placed in the indoor unit 105a, and the capacity of the silencer is varied so that the silencing effect may be maximum depending on the noise frequency, thereby enhancing the silencing effect of the silencer.
Thus, in the air conditioner, the refrigerant circulating in the refrigeration cycle changes in state depending on the pressure and temperature conditions. The refrigerant discharged from the compressor is a gas refrigerant of high temperature and high pressure, and by heat exchange in the condenser, it becomes a liquid refrigerant of high temperature when flowing into pressure reducing means such as an expansion valve. After passing through the pressure reducing means, it becomes a gas-liquid two-phase refrigerant of low temperature, and it further becomes a gas refrigerant of low temperature and low pressure in the evaporator, which gas refrigerant is sucked into the compressor. Depending on the cycle state, the pulsation of the refrigerant discharged from the compressor increases, and the piping vibration and the noise from the condenser coil increase. Also, when the heat exchange in the condenser is insufficient, the refrigerant flowing into the pressure reducing means becomes a gas-liquid two-phase state, and when reducing the pressure, this leads to an increase of noise from the pressure reducing means or the piping before and after it, or an increase of noise from the condenser coil or evaporator coil.
In the prior art, when using the expansion muffler, distributor or silencer member having a special shape of a gradually increasing sectional area for reducing the noise or decreasing the pressure pulsations, an extra space is needed for installing the silencer around the compressor or around the pressure reducing means. However, it is desired to reduce the noise and pressure pulsations effectively while saving space.
Or, to reduce the noise or decrease the pulsations, a porous plate, a partition board or a strainer is inserted in the silencer. Alternatively, the silencer volume is varied by cooperation with the microphone and frequency analyzer, or a sound absorbing material is provided in the silencer. These measures become large and complicated, while it is desired to simplify the construction and curtail the number of constituent parts of the silencer.
Once installed, it is difficult to change the diameter or number of pores of the porous plate in the silencer, the interval between partition boards, or the length of the expanded portion. Also, the reducing effect is smaller in response to noise frequency characteristic changes due to cycle state fluctuations, while it is desired to decrease the noise or attenuate transmission of pressure pulsations regardless of cycle state fluctuations.